1. Field of the Invention
This invention relates to apparatus for separating immiscible liquids of various density, and more particularly concerns a settler for liquid-liquid extractors.
In devices of this type separation of a mixture of phases is done in separation sections immersed in one of the phases.
2. Description of the Prior Art
An increase in the output volume of process solutions necessitates the provision of extraction apparatus having a higher efficiency and smaller mounting area, that is, a higher output capacity per unit volume of the settler.
During the separation of a mixture of phases the efficiency of the process grows as the initial volume of the mixture of phases is separated into layers. The efficiency of separation tends to be higher with the reduction in the height of the layer of the mixture of phases. However, separation in thin layers creates the problem of selecting the optimum ratio between the height of the layer of clean phases and the layer of mixture of phases in the separation section, as well as problems associated with uniform distribution of the mixture of phases in sections and transporting the phases being evacuated from the sections to a common phase boundary.
There is known a settler for liquid-liquid extractors (cf., U.S. Pat. No. 3,868,335) comprising a housing having means for feeding a mixture of phases and evacuating the separated clean phases from the housing. The interior of the housing accommodates separation sections in the form of box-shaped means arranged one above another with a longitudinal and lateral offset, and immersed in one of the phases. Each such box-shaped means has an open top and closed bottom when immersed in the light phase, or a closed top and open bottom when immersed in the heavy phase. It also has four vertical side walls, one of which is provided with a means for feeding a mixture of phases. Arranged in front of this wall is the means for evacuation of one of the phases, whereas provided between this means for evacuation and the wall having the means for feeding the mixture of phases is a partition mounted with a clearance relative to the base or to the top of the arrangement. The settler has a vertical collector of the mixture of phases with the means for feeding the mixture of phases connected to the side wall thereof.
However, this settler suffers from low throughput capacity because the box-shaped means are vertically spaced inside the chamber, and offset longitidinally and laterally, resulting in inefficient utilization of the volume of the settler and, therefore, excessive mounting area. The countercurrent movement of the liquid phase, heavy phase and a mixture of both outside the box-shaped means caused by structural peculiarities of the arrangement for feeding the mixture of phases to the apparatus and evacuating them therefrom also affects the throughput capacity of the settler and results in a larger mounting area.
There is also known a settler for liquid-liquid extractors (cf., U.S. Pat. No. 3,820,954) comprising a housing having a means for feeding a mixture of phases in the form of trays, and a means for evacuating the separated clean phases. Accommodated inside the housing are separation sections in the form of pan-shaped elements arranged in parallel one above another and defining a slot for evacuating one of the phases. Each such element has an open top and closed bottom or open bottom and closed top, and communicates with the means for feeding the mixture of phases. In each pan-shaped means one wall thereof is inclined toward the outside, whereas provided in front of this wall is a means for evacuating one of the phases, inclined toward the inside of the apparatus. Accommodated between the means for evacuating one of the phases and the wall inclined towards the outside is a partition extending from the adjacent pan-shaped means to the phase being evacuated which defines a clearance with the base or top of this pan-shaped means. The settler has a vertical collector of the mixture of phases, a side wall of which is connected to the trays. The distance between the bases of the adjacent pan-shaped means includes the height of the walls and the width of the slot for evacuating one of the phases. The wall which is inclined towards the outside can have a recess to ensure overflow of the mixture of phases.
This settler, however, has an insufficient throughput capacity, on the one hand, because the pan-shaped means are spaced a substantial distance from each other, resulting in excessive height of the chamber. The distance between the bases of the adjacent means, and consequently the thickness of the layers of the mixture of phases and that of the clarified phases is preselected arbitrarily, thereby failing to meet the maximum throughput capacity of the settler. On the other hand, the throughput capacity of the settler is reduced by the countercurrent movement of the separated phases outside the pan-shaped means, especially at the interface between the phases in the settler, where interaction between the phases is of an impact character. Such a movement results in a change in the density of the phase in which these means are immersed, secondary dispersion of the phases, and mutual entrainment of the finely dispersed phases. This in turn necessitates a larger volume of the settler and, accordingly, a larger mounting area.
In addition, the means for feeding the mixture of phases fails to ensure distribution of the mixture of phases in equal volumes necessitating overflow of the mixture of phases from the overlying to underlying pan-shaped means. The provision of a recess in the outwardly inclined wall for ensuring such an overflow can lead to a loss of the phase mixture layer, as the position of the pan-shaped means is deviated from the horizontal. This last disadvantage is especially manifest in the case of employment of elongated pan-shaped means of a limited height.